1. Field of the Invention
Aspects of the present invention relate to an electron emission device, and in particular, to an electron emission device having a predetermined ratio of a width of an electron emission region to a width of an opening of a gate electrode, and an electron emission display using the electron emission device.
2. Description of the Related Art
Generally, electron emission elements are classified into different types depending on the types of electron sources. These include a first type using a hot cathode and a second type using a cold cathode.
The second type electron emission elements using a cold cathode include a field emission array (FEA) type, a surface-conduction emission (SCE) type, a metal-insulator-metal (MIM) type, and a metal-insulator-semiconductor (MIS) type.
The FEA-type electron emission element has an electron emission region and driving electrodes, such as a cathode electrode and a gate electrode. The FEA-type electron emission element is based on the principle that when an electric field is applied to the electron emission region under a vacuum, electrons are easily emitted from the electron emission region. The electron emission region is formed with a material having a low work function or a high aspect ratio, such as a carbonaceous material or a nanometer-sized material.
Several of the electron emission elements are arranged on a first substrate into arrays to make an electron emission device, and the electron emission device is combined with a second substrate having a light emission unit with a phosphor layer and an anode electrode. These components are used to construct an electron emission display.
With the common FEA-type electron emission display, cathode electrodes, an insulating layer, and gate electrodes are sequentially formed on the first substrate, and openings are formed at the gate electrodes and the insulating layer to partially expose the cathode electrodes. Electron emission regions are formed on the cathode electrodes within the openings. Phosphor layers and the anode electrode are formed on a surface of the second substrate facing the first substrate.
The cathode and the gate electrodes are stripe-patterned and formed to cross each other, and each crossed area of the cathode and gate electrodes forms a pixel. The electron emission regions are placed at a predetermined domain of the pixel such that the electron emission regions are spaced apart from each other by a distance.
When predetermined driving voltages are applied to the cathode and the gate electrodes, electric fields are formed around the electron emission regions at the pixels where the voltage difference between the two electrodes exceeds a threshold value, and electrons are emitted from those electron emission regions. The emitted electrons are attracted by a high voltage applied to the anode electrode, and directed toward the second substrate. When the emitted electrons reach the second substrate, the emitted electrons collide against the phosphor layers at the relevant pixels and cause emission of light.
With the above structure, an insulating layer and a focusing electrode may be further formed over the gate electrodes to focus the electron beams. The focusing electrode receives 0V or a negative direct current (DC) voltage of several to several tens of volts, and exerts a repulsive force to the emitted electrons passing through the opening in the gate electrodes and the insulating layer to focus those electrons in the center of a stream of electrons.
Meanwhile, unlike the cone-shaped Spindt-type emitters proposed in the early stages of the electron emitter design, the electron emission region may be formed with a layer having an electron emission material on the surface thereof, mainly through the easily-controlled screen printing process.
Electron beams from the electron emission display having the layered electron emission regions and the focusing electrode include main and sub electron beams within the stream of electron beams. The main electron beams are existent among the stream of electron beams together with sub electron beams. The sub electron beams are placed external to the main electron beams. The width of each of the sub electron beams is larger than that of the main electron beam, and the intensity of each of the sub electron beam is weaker than that of the main electron beam.
Accordingly, the phosphor layer is demarcated into a primary light emission area based on the main electron beam and a secondary light emission area based on the sub electron beam when light is emitted. In case the sub electron beam is widely diffused to neighboring different-colored phosphor layers, those different-colored phosphor layers are excited so that the color purity deteriorates.
The sub electron beam causing the secondary light emission is generated due to the phenomenon where the electrons emitted from the edge of the electron emission region are attracted by the gate electrode, and some of the electrons passing close to the focusing electrode are radically bent to the opposite side by the negative electric field of the focusing electrode.
In order to prevent the sub electron beams from being generated, it has been conventionally proposed that the shape or size of the opening of the focusing electrode should be altered, or the dimension of the focusing voltage should be controlled. However, when the width of the opening of the focusing electrode is enlarged or the focusing voltage is raised to prevent the generation of the sub electron beams, the width of the main electron beam is instead enlarged to thereby increase the width of the primary light emission area, even though the sub electron beams are prevented from being generated, and thereby decreasing the secondary light emission.